Low power-consumption interface apparatus and method for transferring data between a hand-held computer and a desk top computer

ABSTRACT

Disclosed is a computer data interface (100) for connecting a hand-held computer (104) and a desktop computer (102). The computer data interface includes a cable having connectors at each end. A voltage conversion circuit (116) is mounted adjacent to one of the connectors. The voltage conversion circuit receives data signals from the hand-held computer and transmits the signals to the desktop computer at voltage levels compatible with the desktop computer, Similarly, the voltage conversion circuit receives signals from the desktop computer and transmits the signals to the hand-held computer at voltage levels compatible with the hand-held computer.

FIELD OF THE INVENTION

The invention relates to computer communications in general and, morespecifically, to a method and apparatus for providing data transferbetween a hand-held computer and a desktop computer.

BACKGROUND OF THE INVENTION

The use of hand-held computers continues to expand as their capabilitiesincrease and the cost associated with ownership and use of suchcomputers declines. Popular commercially available hand-held or palmtopcomputers include the Casio B.O.S.S.™, Sharp Wizard™, and theHewlett-Packard and Psion series of computers. Hand-held computers havetraditionally been used for data management such as day planning, buttheir use is expanding to electronic mail, spreadsheet, and other tasks.

The most significant advantage of hand-held computers is their relativelight weight and small size. In an effort to minimize the size ofhand-held computers, they typically do not include a full-size keyboard.Ironically, this is perhaps also their most significant disadvantage,because data entry on the smaller keyboards is not as efficient as it ison a desktop computer. A solution to this problem is to interconnect thehand-held computer with a desktop computer using a cable, input the datato be entered into the desktop computer, and then transfer the inputdata to the hand-held computer. Coupling the two computers also allowsdata on the hand-held computer to be transferred to a desktop computerfor archival purposes.

Many of the available hand-held computers operate at voltage levels thatare incompatible with the serial ports on desktop computers. Forexample, logical zero and one on a hand-held computer may be at zero andfive volts, respectively, whereas on a desktop computer the voltagelevels may be in the range of negative 15 volts for a logical zero andpositive 15 volts for logical one. Thus, the voltage levels must beconvened for communications to be successful. A number of computer datainterface solutions have been designed to provide compatibility betweenhand-held and desktop computers. An early solution was a cable thatconnected the Sharp Wizard to an IBM® or IBM-compatible personalcomputer. However, the cable was inconvenient because the voltageconversion circuitry was contained in a relatively bulky housing and wasexternally powered. A more advantageous solution is disclosed in U.S.Pa. No. 5,157,769, assigned to Traveling Software, Inc., the assignee ofthe present application.

U.S. Pat. No. 5,157,769 (the '769 patent) discloses a computer datainterface for connecting a hand-held computer and a desktop computer.The computer data interface includes a cable having connectors at eachend. A voltage level conversion circuit is mounted adjacent to one ofthe connectors for receiving data signals from the hand-held computerand transmitting the signals to the desktop computer at voltage levelscompatible with the desktop computer. Similarly, the level conversioncircuit receives signals from the desktop computer and transmits thesignals to the hand-held computer at voltage levels compatible with thehand-held computer. The level conversion circuit is powered by thedesktop computer to prevent draining the batteries of the hand-heldcomputer.

FIG. 2 of the '769 patent illustrates a voltage level conversion circuitfor transmitting data between an IBM or IBM-compatible personal computer(PC) and a Sharp Wizard hand-held computer. The circuit utilizes aMotorola® MC 145406 integrated circuit to perform voltage conversionsnecessary to allow the two computers to communicate. FIG. 3 of the '769patent illustrates a level conversion circuit that may be used totransmit data between a PC and a Casio B.O.S.S. (Boss) hand-heldcomputer. The primary components in the level conversion circuit of FIG.3 include a number of resistors 42, a transistor 44, a diode 48, and anisolation circuit 52. The transistor 44 has its base connected to thetransmit data TxD line (pin 2 of the PC), its emitter connected toground, and its collector connected to the positive voltage source V+ ofthe PC through one of the resistors 42 as well as the receive line R ofthe Boss through a resistor 50. The isolation circuit is coupled betweenthe collector through two resistors 42 and ground on the Boss.

Briefly, the operation of the level conversion circuit of FIG. 3 is asfollows. When the TxD line (pin 2) is low, positive voltage is appliedto the receive line R of the Boss, i.e., from V+ with the voltage beingclamped by the diode 48. When TxD goes high, the transistor 44 turns on,sinking current to ground and pulling R low. The isolation circuit isneeded to disconnect the ground of the Boss from the PC to ensure thatthe PC does not drain the batteries of the Boss. This may result becausepin 20 will be low when the PC is turned off, and thus current may besourced from R through the resistors 50 and 42 to pin 20.

Transmission in the opposite direction is accomplished using a capacitor34, a diode 36 and an operational amplifier (op amp) 40. The positiveterminal of the op amp 40 is connected to V+ through a resistor 42. Thenegative terminal is connected directly to the transmit line of theBoss. The output of the op amp is connected to the receive line RxD (pin3) of the PC. The capacitor 34 is charged with a negative voltage usingthe TxD line (pin 2). When TxD is low, the output of the op amp is atV+. When TxD is high, the output of the op amp is switched to thenegative voltage supply stored in capacitor 34.

A more recent computer data interface to become commercially availableis the model CE-137T level converter manufactured and sold by SharpCorporation. The CE-137 T level converter may be used to transfer databetween the Sharp Wizard and either a Macintosh computer or a PC in asingle interface. Prior to the CE-137 T level converter, availablecomputer data interfaces typically were designed to connect a hand-heldcomputer to only one of the two types of computers, either Macintosh orPC's, i.e., a first interface would be required for data transfer if auser had a Macintosh computer, and a second, different interface wouldbe required for data transfer if a user had a PC. The CE-137 T levelconverter includes two Motorola integrated circuits to provide voltageconversions between a hand-held computer and both Macintosh computersand PC's.

The computer data interfaces discussed above successfully accomplishvoltage level conversions to allow a hand-held computer to communicatewith a desktop computer. However, prior art computer data interfaceshave typically required integrated circuits. In earlier models, theintegrated circuits were powered externally. In the '769 patent andCE-137 T level converter, the integrated circuits were powered by thedesktop computer. The invention is a simplified circuit design that doesnot require use of integrated circuits or external power, presentingcost, space, and power savings. The power savings may be significant ifthe desktop computer is also battery powered.

SUMMARY OF THE INVENTION

The invention is a system for transmitting data between a low-powertransmitting device having a binary data transmitting element and adesktop computer having a power source and a data receiving element. Alow-power signal from the transmitting device represents a logical oneand the absence of a signal represents logical zero. The systemcomprises (a)a switching transistor, coupled between the power sourceand the data receiving element; (b) a control component, coupled to thetransistor, for establishing a control voltage that dictates thethreshold at which the transistor turns on and off, and (c)a componentfor conveying data from the data transmitting element of thetransmitting device to the transistor, wherein the transistor turns onwhen the low-power signal is conveyed from the transmitting devicecausing current to flow between the power source and the data receivingelement.

In accordance with other aspects of the invention, the transmittingdevice is a hand-held computer. Further, the component for conveyingdata from the data transmitting element of the transmitting device tothe transistor is a cable.

In accordance with other aspects of the invention, the component forconveying data from the data transmitting element of the transmittingdevice to the transistor is a wireless communications system.

In accordance with still further aspects of the invention, the systemincludes a method for transmitting data between a hand-held computerhaving a data transmitting element and a desktop computer having apositive voltage source, a negative voltage source, and a data receivingelement. The method comprises the steps of: (a) coupling the datareceiving element to the negative voltage source of the desktopcomputer; (b) coupling a transistor between the data receiving elementand the positive voltage source; (c) providing a data path between saidtransistor and the data transmitting element of the hand-held computer;and (d) using the data transmitting element to transmit digital datafrom the hand-held computer to the desktop computer wherein when a firstlogic state is being transmitted said transistor is turned on and when asecond logic state is being transmitted said transistor is off.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 illustrates connecting a desktop computer to a hand-held computerusing a data transmitting system in accordance with the invention;

FIG. 2 is a schematic diagram of a first exemplary embodiment of theinvention for connecting a PC to a Casio B.O.S.S.;

FIG. 3 is a schematic diagram of a second exemplary embodiment of theinvention for connecting a PC to a Sharp Wizard; and

FIG. 4 is a block diagram showing the connections necessary to use thecircuits shown in FIGS. 2 and 3 with a Macintosh computer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIG. 1, a computer data interface 100 in accordancewith the invention connects a desktop computer 102 with a hand-held orpalmtop computer 104. The hand-held computer may be, for example, aCasio B.O.S.S., Sharp Wizard, Hewlett-Packard, or Psion hand-heldcomputer. Throughout the specification, the term desktop computer ishereby defined as including IBM, IBM compatible, Apple, and similarmicrocomputers, whether they be designed for the desktop use only orportable computers. Further, the term "personal computer" (PC) is usedthroughout the specification to refer to IBM and IBM-compatiblecomputers and the term "Macintosh" is used to refer to computersproduced by the Apple Corporation. Each computer will typically includea display, keyboard, processor, and volatile and nonvolatile memories.Further, the desktop and hand-held computers 102 and 104 includecommunications ports 106 and 108, respectively, that facilitatecommunications with other computers and peripheral devices.

In one embodiment, the computer data interface includes a cable 110having connectors 112 and 114 that may be connected to thecommunications ports 106 and 108, respectively, to provide datatransmission between the desktop and hand-held computers. Alternatively,the computers may communicate through a wireless link, as describedfurther below. The computer data interface also includes a levelconversion circuit 116, preferably housed with or adjacent to theconnector 114, that enables the desktop and hand-held computers tocommunicate effectively. Software running on each computer interpretsthe signals being sent back and forth across computer data interface.Such software is known in the art, and thus is not described herein.

FIG. 2 illustrates a first exemplary embodiment of the computer datainterface 100 for use in connecting a PC to a Casio B.O.S.S. (Boss) inaccordance with the invention. As shown on the left, the computer datainterface is connected to the PC using either a conventional DB-25connector or a conventional DB-9 connector. The specific pins on theDB-25 and DB-9 that are used by the computer data interface and theirfunctions are listed below:

    ______________________________________    DB-25 Connector               DB-9 Connector                             Function    ______________________________________    Pin 2      Pin 3         T × D (transmit data)    Pin 7      Pin 5         Ground    Pin 20     Pin 4         DTR (+V)    Pin 3      Pin 2         R × D (receive data)    Pins 4 & 5 Pins 7 & 8    RTS & CTS (-V)    ______________________________________

Opposite the DB-25 and DB-9 connectors, the computer data interface isconnected to a Casio Boss through a phono plug (connector 114) thatincludes receive (R), transmit (T), and ground (B) contacts.

To transfer data from the PC to the Boss, the level conversion circuit116 includes a transistor Q1 having its base connected to the TxD pin ofthe connector 112 through a resistor R1 as well as to ground of the PCthrough a resistor R2. The collector of transistor Q1 is connected tothe receive contact R on connector 114. The emitter of transistor Q1 isconnected to ground on the PC through a resistor R3 and directly toground on the Boss via the ground contact B of connector 114. Thetransistor Q1 is preferably an NPN transistor. Suitable values for theresistors R1, R2, and R3 are 4.7 kiloOhm (kΩ), 4.7 kΩand 270 Ω,respectively.

The operation of the level conversion circuit may be briefly describedas follows: By convention, contact R on connector 114 is kept highinternally by the Boss. When data are not being transmitted by the PC orwhen sending a logical zero, the TxD line of the PC is low andtransistor Q1 is in an off state. In this instance, transistor Q1 is an"open-collector," and thus has no effect on R. Conversely, when alogical one is being transmitted, the TxD line becomes high, turningtransistor Q1 "on" and pulling R to ground. Software running on the PCand Boss controls the operation of the computers to change and sense,respectively, the voltage levels on the TxD and R lines, therebyaccomplishing data transfer.

It has been found that to ensure proper operation of the levelconversion circuit 116, the transistor Q1 must be in relatively closeproximity to the Boss. Otherwise, interference on the line between theBoss and the transistor Q1 may cause R on the connector 114 to be pulledlow, causing spurious results during data transfer. Thus, the levelconversion circuit 116 is preferably placed adjacent to the connector114, with the length of cable 110 extending from circuit 116 toconnector 112.

In transferring data from the Boss to the PC, the invention allows theBoss or other computer to send data to a PC without requiring anyexternal power and using very few discrete components. As will beunderstood from the following description, this is accomplished byestablishing a path between the positive voltage source of the PC andits receive line RxD of the PC when a logical one is to be transmitted,and isolating the positive voltage source otherwise. In accordance withthe invention, a low power signal from the hand-held device is used toestablish the path during transmission of a logical one. Since the PC'sown power is used to drive the receiving line of the PC, the powerrequired of the hand-held computer to communicate with the PC isnegligible.

The basic components in the level conversion circuit 114 that arerequired to transfer data from the Boss to the PC include a field-effecttransistor (FET)Q2, a zener diode D1, and a resistor R5. The resistor R5connects RxD of connector 112 to the negative voltage source RTS of thePC. The gate of the FET Q2 is connected to contact T of the connector114 through a resistor R6 and to ground on the connector 112 through azener diode D2. Specifically, the anode of diode D2 is directlyconnected to ground on the PC and connected to ground on the Bossthrough the resistor R3. The cathode of diode D3 is connected to thegate of transistor Q2. The drain of Q2 is connected to the Rx pin onconnector 112 through a resistor R7.

Specific connections for the source of transistor Q2 include aconnection between the cathode of diode D1 and the source, and aconnection from the anode to ground of the PC. The source of transistorQ2 is also connected to the positive voltage source DTR (+V) of the PCthrough a resistor RS. Finally, the source is connected to the cathodeof the diode D2 through a resistor R9.

With regard to the operation of the level conversion circuit 116 duringdata transfer from the Boss to the PC, the diode D1 sets the thresholdfor turning Q2 on and off by clamping the positive voltage source DTR toapproximately 5.1 volts. When T is high, the potential at the gate of Q2will be around 3-5 volts, and Q2 will be in an off state. Thus, there isno current flowing between the source and drain, and RxD will continueto be pulled low by the negative voltage source RTS (-V) of the PC. WhenT goes low, Q2 turns on, and Rx is connected to the clamped positivevoltage source DTR, pulling Rx to a high state. In this manner, datatransfer is accomplished with the logistics handled by software.Transistor Q2 is preferably an FET rather than another type oftransistor because field-effect transistors draw little or no current,saving the batteries on the Boss. Also, use of an FET is advantageousbecause the drain of the FET can be at a negative voltage while stillallowing the threshold to be properly set such that the FET may beswitched on and off using the transmit line T of the Boss. In oneembodiment, the diodes D1 and D2 are rated at 5.1 and 9.1 volts,respectively. A suitable value for the resistors R5 and R6 is on theorder of 4.7 kΩ. A suitable value for resistors R7 and R8 is 270 Ω; andresistor R9 may be on the order of 1 MΩ.

FIG. 3 illustrates a second exemplary embodiment of a computer datainterface 140 for use in connecting a PC to a Sharp Wizard in accordancewith the invention. As in FIG. 2, the computer data interface isconnected to the PC using either a DB-25 connector or DB-9 connector.The computer data interface is connected to a Sharp Wizard using a15-pin interface connector 142. The specific pins on the connector 142and each pin's function is listed below:

    ______________________________________    15-Pin Connector  Function    ______________________________________    Pin 2             T × D (transmit data)    Pin 7             Ground    Pin 10            VC (+V)    Pin 3             R × D (receive data)    ______________________________________

The computer data interface 140 includes a voltage level conversioncircuit 144 that has many of the same components, performing the samefunctions, as the circuit previously described. These components haveidentical reference numerals. To transfer data from the PC to the SharpWizard, the voltage conversion circuitry includes an additionaltransistor Q3 that is connected between the transistor Q2 and theresistor R6. Specifically, the base of transistor Q3 is connected toresistor R6, the emitter is connected to the gate of transistor Q2, andthe collector is connected to ground, i.e., pin 7 of the connector 142.It has been found that the data signals transmitted by the Wizard arethe inverse of those from the Boss. The transistor Q3 acts to invertdata to be sent as it is transmitted, so that the transistor Q2 performsas described above.

The circuitry for transferring data from the PC to the Wizard includes adiode D3, a Schottky diode D4, and a pair of resistors R10 and R11. Theanode of the diode D3 is connected to the TxD pin of connector 112. Thecathode of diode D3 is connected to the anode of diode D4 through theresistor R10. The diode D3 essentially prevents negative voltage fromreaching the receive line RxD of the Wizard. Thus, when a logical zerois present on the TxD line of connector 112, the voltage at RxD of theWizard will be at or near zero volts, and perceived as logical zero tothe Wizard. The resistors R10 and R11 act as a voltage divider when alogical one is being sent by the PC. The result is that the voltagelevels presented to the Wizard will be of sufficient magnitude torepresent a logical one to the Wizard, while still being within theSharp Corporation's specifications establishing maximum voltages thatmay be applied to the Wizard. The diode D4 provides added assurance thatmaximum voltage tolerances are met. A suitable value for resistors R10and R11 is 270 Ω.

FIG. 4 illustrates the pin connections necessary to modify the computerdata interfaces illustrated in FIGS. 2 and 3 for use with Macintoshcomputers. Specifically, Macintosh computers typically include a Din-8connector 150 having the following pins:

    ______________________________________    Din-8 Connector  Function    ______________________________________    Pin 2            T × D- (transmit data)    Pin 4            GND (ground)    Pin 1            HSKO (+V)    Pin 3            R × D- (receive data)    ______________________________________

By connecting the pins of connector 150 as shown in FIG. 4, i.e., TxD-to Tx, ground to ground, HSK0 to DTR, and RxD- to Rx, the computer datainterface may be used to interface a Macintosh with a Boss using thevoltage conversion circuit 116 of FIG. 2 or a Wizard using the voltageconversion circuit 144 of FIG. 3. In addition to the above connections,the RxD- pin is connected to ground through a resistor R12, which may beon the order of 4.7 kΩ. Unlike PC's, the Din-8 connector does notprovide access to a negative power supply. However, pulling the Rx lineof the voltage conversion circuit to ground, as opposed to -V in the PCversion, is adequate. For use with a Macintosh the voltage conversioncircuits generally operate in the same manner described above.

As will be appreciated by those skilled in the art, the computer datainterface is relatively inexpensive to build, does not require anyexternal power, and does not require integrated circuits. It will alsobe appreciated that the computer data interface may be used to connectdesktop computers to other types of computers besides the Boss andWizard. Along this line, the teaching of the invention may be used byvirtually any device that a designer wishes to have communicate withdesktop computers, e.g., sensors for temperature, humidity, etc.Virtually no power is required of the communicating device because thedesktop computer's power is used to drive the transmit line. Thisfeature is particularly advantageous when the invention is used withbattery-operated devices. Further, the computer data interface mayincorporate wireless communications technology to provide a data pathbetween the computers and thus alleviate the necessity of a cable.

While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A computer datainterface for transmitting data between a low-power transmitting devicehaving a binary data transmitting element, with a presence of alow-power signal from the low-power transmitting device representing alogical one and an absence of the low-power signal representing alogical zero, and a computer having a power source and a data receivingelement, comprising:a voltage level conversion circuit without anintegrated circuit, the voltage level conversion circuit including aswitching transistor coupled between the power source and the datareceiving element and having an off-state in which the switchingtransistor is substantially an open-circuit and an on-state in which acurrent flows between the power source and the data receiving element; adiode coupled to the switching transistor for establishing a thresholdvoltage at which the switching transistor switches between the on-stateand the off-state, the threshold voltage corresponding to the presenceof the low-power signal from the low-power transmitting device; and adata path for conveying data from the binary data transmitting elementof the low-power transmitting device to the switching transistor,wherein the switching transistor switches to the on-state when thelow-power signal is conveyed from the low-power transmitting device,thereby causing the current to flow between the power source and thedata receiving element.
 2. The computer data interface of claim 1wherein the low-power transmitting device is one of a hand-heldcomputer, a palmtop computer, a personal organizer, and a personalassistant.
 3. The computer data interface of claim 1 wherein the datapath for conveying data from the binary data transmitting element of thelow-power transmitting device to the switching transistor is a cable. 4.The computer data interface of claim 1 wherein the computer is one of adesktop computer, an IBM personal computer, an IBM-compatible computer,and an Apple Macintosh computer.
 5. The computer data interface of claim1 wherein at least one of the computer and the low-power transmittingdevice is powered by a battery.
 6. The computer data interface of claim1 wherein the voltage conversion circuit is positioned in a closeproximity to the low-power transmitting device.
 7. The computer datainterface of claim 1 wherein the switching transistor is a field-effecttransistor.
 8. A method for transmitting data between a hand-heldcomputer having a data transmitting element and a desktop computerhaving a positive voltage source, a negative voltage source, and a datareceiving element, the method comprising:coupling the data receivingelement to the negative voltage source of the desktop computer; couplinga normally nonconducting field-effect transistor between the datareceiving element and the positive voltage source; providing a firstdata path between the normally nonconducting field-effect transistor andthe data transmitting element of the hand-held computer; andtransmitting a first logic state and a second logic state from thehand-held computer to the desktop computer, wherein when the first logicstate is being transmitted the normally nonconducting field-effecttransistor conducts a current between the positive voltage source andthe data receiving element and when the second logic state is beingtransmitted the normally nonconducting field-effect transistor does notconduct the current between the positive voltage source and the datareceiving element.
 9. The method of claim 8, wherein the hand-heldcomputer further includes a data receiving element and the desktopcomputer includes a data transmitting element, the method furtherincluding:providing a second data path between the data transmittingelement of the desktop computer and the data receiving element of thehand-held computer; and transmitting digital data from the datatransmitting element of the desktop computer through the second datapath to the data receiving element of the hand-held computer.
 10. Themethod of claim 9 wherein the first data path and the second data pathis provided by a cable.